In recent years, smart phones or tablet PCs or the like using a touch panel appear on the market, and demand for reduction in thickness, increase in transmittance as an optical characteristic, and reliability against heat and moisture absorption is increasing.
As a method achieving the reduction in thickness, there is a tendency to apply an on-cell manner in which a display cell such as LCD or EL or the like and a touch panel are integrated. However, with regard to the structure in which the display cell and the touch panel are integrated, after the display cell is fabricated, a touch sensor is fabricated on a surface of the display cell, and thus, the risk during fabrication is high and problems occur during the implementation. A solution to the above problems, which is to laminate a sensor substrate having as thin thickness as possible to the display cell, may obtain an effect similar to that of the on-cell manner.
However, if a thin film is used as the material for the sensor substrate, the resistance value of an electrode has to be decreased in the case of requiring high performance characteristics. In this case, a process performed at a high temperature is required, and in this regard, there is limitation to the thin film.
As required by the circumstance, the present inventors invented a flexible glass substrate described in Patent Literature 1. However, as the above-described requirement from the market is increasing, a touch panel which is thinner and lighter, has a high transparency in order to extend the lifespan of a battery, and has high performances and reliability, is desired to be developed.
However, the flexible glass described in Patent Literature 1 invented by the present investors is a product for thinning a glass to a maximum extent, and it is very difficult to further thin the glass. On the other hand, the thinned glass becomes easily broken so that a base film should be attached, and thus, the base film is a necessary constituent element. Therefore, the current circumstance is that the thickness of the base film has to be thinned in order to simply thin the flexible glass. If the thickness of the base film becomes thinner, the entire thickness will become thinner, and the transmittance as an optical characteristic will also be improved.
Under such a circumstance, though there are difficulties in meeting requirements from the market, the present inventors invented the present invention by changing minds.
Prior Art Document
Patent Literature
Patent Literature 1: Japanese Patent No. 4565670